Experimental chemotherapy has been the mainstay of treatment offered to patients diagnosed with surgically unresectable advanced cancers, or cancers refractory to standard chemotherapy and radiation therapy. Of the more effective classes of drugs, curative properties are still limited. This is because of their relatively narrow therapeutic index, restricted dosage, delayed treatments and a relatively large proportion of only partial tumor reductions. This state is usually followed by recurrence, increased tumor burden, and drug resistant tumors.
Several cytoprotective agents have been proposed to enhance the therapeutic index of anticancer drugs. For methotrexate toxicity, such agents include asparaginase, leucovorum factor, thymidine, and carbipeptidase. Because of the extensive use of anthracyclines, specific and non-specific cytoprotective agents have been proposed which have varying degrees of efficacy; included are corticosteroids, desrazoxane and staurosporin. The latter is of interest in that it includes a G1/S restriction blockade in normal cells. (Chen et al., Proc AACR 39:4436A, 1998).
Cisplatin is widely used and has a small therapeutic index which has spurred investigation and search of cytoprotectants. Among the cytoprotectants for cisplatin with clinical potential are mesna, glutathione, Na-thiosulfate, and amifostine (Griggs, Leuk. Res. 22 Suppl 1:S27-33, 1998; List et al., Semin. Oncol. 23(4 Suppl 8):58-63, 1996; Taylor et al., Eur. J. Cancer 33(10):1693-8, 1997). None of these or other proposed cytoprotectants such as oxonic acid for fluoropyrimidine toxicity, or prosaptide for paclitaxel PC12 cell toxicity, appears to function by a mechanism which renders normal replicating cells into a quiescent state.
What is needed are cytoprotective agents which are effective in protecting animals, inclusive of humans, from the cytotoxic side effects of chemotherapeutic agents.
Unrelated to the foregoing, styryl sulfones having pharmaceutical utility as anticancer agents have been reported in WO/99/18068, the entire disclosure of which is incorporated herein by reference. The compounds inhibit tumor cell growth by inducing tumor cell death without killing normal cells. The styryl sulfones are effective in a broad range of tumor types. Without wishing to be bound by any theory, it is believed that the styryl sulfones affect the Mitogen Activated Protein Kinase (MAPK) signal transduction pathway, thereby affecting tumor cell growth and viability.